Semiconductor Diode – Definition, Characteristics, Applications

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Semiconductor diode definition – type of diode, which contains “p-n junction” made of semiconductor materials. It’s double-ended, nonlinear element where the end attached to the “p” layer (+) is called anode and “n” layer () – cathode.

semiconductor diode symbolSemiconductor diode symbol

The main advantage of this electronic component is current flowing only in one direction (from anode to the cathode) after forward-biasing the “p-n junction”. However, in the opposite direction (reverse bias) current doesn’t flow and we could call this as the electric valve. Diode is constructed from two semiconductors, which were doped in different proportions – “p” and “n” types. They together form the p-n junction. The “n” layer with donor dopants has excess of electrons where the “p” layer (acceptor dopants) – have deficiency of them. After combining these on semiconductor diode together, a proportional distribution of electrons begins. Electrons, which previously lacked in “p” layer are transferred there from “n” layer. In this way region called depletion region that prevents the electric flow is formed. With passing time, technological requirements were increasing what resulted in formation of new types of diodes.

semiconductor diode

When semiconductor is combined with the corresponding metal, we acquire MS junction (metal-semiconductor), which also possesses rectifying properties (current conduction in one direction) – it is used for example in Schottky diode. MS junctions can have one of two current-voltage characteristics:

  • Unsymmetrical non-linear
  • Symmetrical, linear

MS junction properties depends mainly on the surface state of semiconductor and on the output work difference of electrons from metal and semiconductor itself. Schottky diode is mainly used in systems that require short switching time (small junction capacitance Cj of diode has decisive impact) with frequencies up to several tens of GHz.

semiconductor diode characteristics

Current-Voltage characteristic of semiconductor diode

Illustration of differently biased P-N junctions:

PN junction after reverse bias

PN junction reverse-biased

PN junction in state of thermodynamic equilibrium

PN junction in state of thermodynamic equilibrium

PN junction after forward bias

PN junction forward-biased

How to determine where is the anode and where is the cathode?

Simple multimeter can be used to determine the polarity of a diode. There are at least three ways to do this but I will show two most popular that can be used with cheap multimeters:

a) Using ohmmeter (2kΩ range):

semiconductor diode ohmmeter forward

Forward-bias: Ohmmeter will indicate approximate forward voltage of the diode (near 0,7V)

semiconductor diode ohmmeter reverse

Reverse-bias: Ohmmeter indicates “1” what means very high resistance

You can also use “diode check” function (diode symbol on the multimeter) but the result will be the same as the above with using ohmmeter.

b) Using VDC measurement function:

semiconductor diode voltmeter forward

Forward-bias: Multimeter should indicate voltage drop of approximately 0,7V for silicon diodes

semiconductor diode voltmeter reverse

Reverse-bias: Multimeter will indicate the approximate full voltage of the supply

Common types of semiconductor diodes (and their main functions):

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I'm Michael. Me and my friend John are students of electronics. We are creating this site to help students and any interested people understand electronics.

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